Optical networks traditionally consist of a collection of static, inter-nodal communication links located on a ring or mesh. In such a network, network nodes include (a) transmitters having multiplexers (MUX's) that combine multiple channels with different wavelengths into a combined WDM optical signal that is transmitted to remote nodes on the network, as well as (b) receivers having demultiplexers (DMUX's) that recover individual wavelength channels from previously multiplexed WDM optical signals received from remote nodes on the network. The transmitters and receivers typically operate at fixed central frequencies, and the MUX's and DMUX's traditionally have fiber port connections that require pre-assigned wavelengths that cannot be varied. Reconfiguring such networks in order to create (or tear down) connections between nodes typically requires human intervention. For example, a technician may need to add or remove equipment (e.g. transmitters) and rearrange fiber connections to various optical components (e.g. MUX's or DMUX's) at one or more nodes.
One approach to achieve reconfigurability involves the use of optical add/drop multiplexers (OADM's) that can be remotely controlled in order to add or drop an optical signal to a client, and selectively pass an optical signal (of a specific optical wavelength) through the node without being affected. The various major components in such OADM's currently can be obtained in various discrete technologies. For example, 2×2 switches as well as optical cross-connects (OXC's) can be made of thermo-optic, electro-optic, or micro-electro-mechanical systems (MEMS). The MUX's/DMUX's can be made of multi-layer dielectric filters, arrayed waveguide gratings, or bulk-optic diffraction gratings. Unfortunately, building OADMs out of discrete components is very expensive, and many of these discrete technologies are not well suited for integrated fabrication.
A recent improvement in the OXC component of an OADM is described in patent application entitled “Integrated Wavelength Router”, Ser. No. 10/035,628 filed Nov. 1, 2001, on behalf of Christopher R. Doerr, which application is assigned to the same assignee as the present application, and which is hereby incorporated herein by reference. In the aforementioned application, a 1×K wavelength-selective cross connect (WSC) comprises a demultiplexer arranged to receive an input WDM signal containing multiple wavelengths, and apply its output, namely, the separated the wavelengths, to a binary tree, i.e., at least two stages, of interconnected 1×2 switches. The switches are integrated, and have their outputs crossing each other at each stage. The outputs of the switches in the final stage are applied to, and combined in, K multiplexers, which provide the outputs of the router. If desired, a set of shutters can be interposed in the waveguides leading to the multiplexer inputs, thereby providing additional isolation. The Doerr arrangement advantageously can be fabricated in a small area and therefore implemented in an integrated fashion.
Notwithstanding the foregoing, other elements of the OADM have not, to date, been arranged in an integrated architecture, so that the remote reconfiguration functionality that is desired has not been achieved.